In the medical field, syringes are used for a variety of functions. However, syringes generally operate in one of two manners: (1) aspirating, or extracting a fluid from a subject; and (2) injecting a fluid into a subject. Conventional syringes require two separate components for aspirating or injecting a fluid, specifically a syringe body and a plunger. The syringe body includes an attached needle on one end and a reservoir on the other. The reservoir is used to hold either a fluid to be injected or a fluid that has been aspirated. The plunger fits into the reservoir end forming an airtight seal and thus creating a vacuum in the reservoir. By moving the plunger, a person operating the syringe can either inject a fluid by moving the plunger further into the reservoir, or aspirate a fluid by moving the plunger further out of the reservoir.
A conventional syringe has inherent drawbacks. Some applications of a syringe require steady application of pressure both at the needle end and at the plunger. Injecting a fluid directly into a blood vessel, for example, requires steadiness at the needle. By applying pressure to the end of the plunger, any small lateral movements of the plunger results in an exaggerated movement at the needle tip. This exaggerated movement can damage or destroy a blood vessel. Another situation involves injection or aspiration from a small organ such as the eye. Any movement may induce unwanted side effects.
Another drawback of conventional syringes is that some applications require the use of two hands. If a patient is moving uncontrollably (e.g., due to extensive trauma or shock), a person operating the syringe may need to use one hand to steady the needle tip and ensure the needle remains inserted into the subject being injected, while the operator's second hand is used to operate the plunger end. Situations like this typically require an assistant to stabilize the subject being injected while the operator controls the syringe.
Aspirating with a conventional syringe nearly always requires the use of two hands, unless the syringe has been previously modified. One hand holds the syringe body steady while the second hand extracts the plunger from the reservoir end of the syringe body. The movements required to aspirate with a typical syringe dictate that two hands be used to perform the aspirating safely.
In the above discussion, the common fundamental problem with traditional syringes is the inability to safely operate the syringe with one hand during specific applications such as injecting a moving subject or aspirating fluid from a subject. Another fundamental problem is the inability of the traditional design to address injection/aspiration into a small delicate organ such as the eye with one hand while maintaining stability of the eye/head.